This invention relates to refrigerating systems having a plurality of evaporators and formed as a refrigerant circuit of the refrigerant compression type, and more particularly to a refrigerating system of the type described which makes it possible to effect defrosting of any evaporator as desired with high efficiency when frost is formed on the surfaces of the evaporators as a refrigerating operation is performed.
A refrigerating system of the compression type having a refrigerant compressor, a condenser, a plurality of evaporators and a plurality of expansion valves each belonging to one of the evaporators is generally formed as a closed circuit in which a refrigerant (R-12, R-22 or R-502) is sealed. This type is refrigerating system develops frost formation in the evaporators as a refrigerating operation is performed. Heavy frost formation lowers the refrigerating ability of the system, so that it is necessary to effect defrosting depending on the degree of frost formation on the surfaces of the evaporators.
The refrigerating system in which the present invention can be incorporated is mainly of the type which is used as a refrigerating system for supermarkets and the like. In this type of refrigerating system, a condensing unit consisting of one or a plurality of compressors has connected thereto a plurality of evaporator units (mounted in show-cases of a store).
When a defrosting operation is performed in this type of refrigerating system, defrosting may be effected with a single evaporator as a unit and the rest of the evaporators perform a refrigerating operation. Alternatively, a plurality of evaporators may be formed into a block in a refrigerant circuit, and the evaporators belonging to this block may be subjected to defrosting as a unit, with the evaporators belonging to other blocks continuing in refrigerating operation.
In the description set forth hereinafter and in the claims, the term "unit evaporator means" is used which refers to the unit of an evaporator or evaporators in which defrosting is effected when the system is operated for performing defrosting. Therefore, the term should be understood to include either a single evaporator or a plurality of evaporators belonging to a unit block.
In one type of refrigerating system known in the art which effects defrosting of the evaporators in accordance with the aforesaid principle, a refrigerant circuit is formed in which a branch line is connected at one end thereof to the high pressure gas refrigerant outlet passage between the refrigerant compressor (hereinafter referred to as a compressor) and the condenser for taking out a high pressure gas refrigerant for effecting defrosting, each unit evaporator means is connected at the compressor side thereof either to the suction side of the compressor or to the other end of the branch line by switching from one to the other by means of flow passage change-over valves, and a parallel circuit of an electromagnetic valve and a check valve is suitably connected through the expansion valve side passage of each unit evaporator means to the receiver through a throttle. When all the unit evaporator means operate to effect refrigeration (hereinafter referred to as a refrigerating mode), the compressor side of each unit evaporator means is connected to the suction side of the compressor through the associate flow passage changeover valve to function as an ordinary refrigerant circuit. When unit evaporator means of any number as desired of all the unit evaportor means are subjected to defrosting while the rest of the unit evaporator means perform a refrigerating operation (hereinafter referred to as a defrosting mode), the flow passage change-over valves of the unit evaporator means to be defrosted are actuated to connect the same to the branch line, so that a portion of the high pressure gas refrigerant exhausted from the compressor is passed to such unit evaporator means to effect defrosting thereof while the rest of the unit evaporator means continue to perform a refrigerating operation.
The refrigerating system which effects defrosting of the evaporators in accordance with the aforesaid principle is required to satisfy the following requirements. Such system should be able to positively produce a refrigerant in a gaseous state of high pressure which enables defrosting to be effected when the system operates in the defrosting mode. The flow of the refrigerant in a gaseous state of high pressure used for defrosting to the unit evaporator means to be defrosted should be promoted. The efficiency with which defrosting is effected should be increased. And the supply of refrigerant to the rest of the unit evaporator means should be ensured so as to enable such evaporators to perform a refrigerating operation by feeding a sufficiently high flow rate of refrigerant to prevent a reduction in refrigerating efficiency.
This type of refrigerating system is disclosed in U.S. Pat. Nos. 3,150,498, 3,343,375, 3,427,819 and 3,645,109.
The system disclosed in U.S. Pat. No. 3,150,498 is characterized by the provision of a throttle valve mounted between the condenser and the receiver for causing the defrosting high pressure gas to flow, so as to enable the condensate produced as the result of defrosting to be recovered and collected in the receiver.
U.S. Pat. No. 3,343,375 is directed to a system which is characterized in that a liquid conduit from the liquid line is inserted in a branch line connected to the outlet passage of the compressor to enable the refrigerant in a liquid state from the liquid line to be sucked by the Venturi effect into a refrigerant in a gaseous state of high pressure for effecting defrosting which is taken out through the branch line, so as to bring the refrigerant in a gaseous state of high pressure to a state of a gas of high pressure which is almost saturated.
In U.S. Pat. No. 3,427,819, there is disclosed a system having a feature in the manner of production of the refrigerant in a gaseous state of high pressure, in which system the gas of high pressure almost saturated which is taken out from the upper portion of the receiver is used as the refrigerant in a gaseous state of high pressure for effecting defrosting.
The system disclosed in U.S. Pat. No. 3,645,109 is characterized in that a throttle is provided downstream of the receiver for imparting differential pressure to the flow of the refrigerant in a gaseous state of high pressure for effecting defrosting by the action of the throttle, and the refrigerant in a gaseous state is drawn toward the suction side of the compressor through a float switch from the header for the evaporators or from the upper portion of a vessel mounted independently of the receiver, so that the refrigerant in the liquid state condensed by the defrosting action can be introduced into the header or the vessel.
In the aforesaid system, the refrigerant which has been changed from the gaseous state to the liquid state by condensation as the result of a defrosting operation is caused to flow into the header for the evaporators or the reservoir vessel mounted independently of the receiver. In such system, it is necessary to provide a space of a large area for storing the gaseous refrigerant in order to positively separate the gaseous phase from the liquid phase in the refrigerant introduced into the header or the reservoir vessel, so that only the flash gas can be made to flow to the suction side of the compressor.